The invention relates generally to a photolithography method for making a semiconductor device, for example, a diode containing nonvolatile memory array.
In order to fabricate 45 nm and 80 nm features, one prior art process uses a hard mask stack shown in FIG. 1. The stack consists of a layer of organic hard mask 103, also called advanced patterning film (APF), a layer of Dielectric Anti-Reflective Coating (DARC) 106, such as silicon oxynitride, on top of organic hard mask 103, and a Bottom Anti-Refection Coating (BARC) 109 layer, such as an organic BARC layer, on top of DARC layer 106. A photoresist 111 is located above the BARC layer.
A combination of the DARC 106 and the BARC 109 layers are used to ensure proper suppression of wafer reflectivity. Resist patterns 111 are first used to define the BARC 109 and the DARC 106 that in return is used to define the organic hard mask 103, followed by patterning a device layer 101. The thickness of the DARC 106 layer generally ranges from 60 to 80 nm, primarily driven by the need of providing sufficient masking for patterning the organic hard mask 103. For example, as shown in FIG. 1, DARC layer 106 may be 60 nm thick and have a refractive index of real part (n) of 1.82 and imaginary part (k) of 0.175.